Sorbent for treatment of effluent gas stream

ABSTRACT

A process for producing a sulfur sorbent composition in a mixer having a mixer paddle an energy supply is disclosed which includes hydrating an alkaline earth metal oxide in an aqueous solution containing a promoting additive selected from a group consisting of urea and mixtures of urea with a water soluble iron salt under high intensity mixing conditions with the mixer wherein the mixer is operated at a mixer paddle tip velocity of at least 500 ft/min and a mixer energy input of at least 3.5 kW-h per ton of sorbent so as to produce a sulfur sorbent composition having the following physical and chemical properties: alkaline earth metal (wt.%)--40-52, molar ratio of promoting additive to alkaline earth metal--0.001-0.2, bulk density (g/ml)--0.35-0.75, surface area (m 2  /g)--5-25, pore volume (cc/g)--0.05-0.14 and mean particle size (μm)--4.

BACKGROUND OF THE INVENTION

The present invention relates to a process for producing a sulfursorbent composition for use in removing sulfur oxides from a stream ofeffluent gas and the resultant sorbent produced.

Desulfurization of effluent gas is achieved by various procedures knownin the art. One known procedure is to treat the effluent gas withsorbents, such as calcium carbonate or calcium hydroxide.

Such sulfur sorbents are the subject, for example, of U.S. Pat. No.4,424,197 to Powell et al. This patent discloses the use of CaO preparedby flash calcination of a special type of aragonite sand, thusgenerating a CaO product which reacts with SO₂. This procedure haseconomic drawbacks due to the special raw material required and thenecessary flash calcination procedure.

When commercial calcium carbonate or hydroxide is used, however, sulfurreactivity is generally unsatisfactory. Various approaches have beenreported wherein improvement of sulfur reactivity is attempted.

Several disclosures have been made regarding the use of urea as anadditive to hydrated calcium in order to remove NO_(x) compounds fromgas streams, or to simultaneously remove SO₂ and NO_(x).

U.S. Pat. No. 4,731,233 disclose in which urea is incorporated intoCa(OH)₂ by dissolving urea into the hydration water. The '233 patentdiscloses that the urea additive does not harm the reactivity of thesorbent towards SO₂. No particular hydration procedures are indicated inthe '233 patent.

Such urea promoted sorbents, prepared conventionally, yield sorptionrates up to a maximum of about 60% at molar ratios of Ca to sulfur ofabout 2.

Metal salts have been used as additives to try to improve the sulfurreactivity of calcium based sorbents. For example, Muzio et al presenteda paper entitled "The Effectiveness Of Additives For Enhancing SO₂Removal With Calcium Based Sorbents" at the 1986 Joint Symposium on DrySO₂ and Simultaneous SO₂ /NO_(x) Control Technologies (EPRI ProceedingCS-4996, Vol. I, pp. 13-23). This paper reports that the incorporationof iron into the hydration water had no significant effect on SO₂capture.

Slaughter et al. presented a paper entitled "Enhanced Sulfur Capture ByPromoted Calcium-based Sorbent" at the aforesaid 1986 Joint Symposium(EPRI Proceedings CS-4996, Vol. I, pp. 12-24). This paper indicates thatthe physical mixture of Fe_(2O) ₃ to Ca(OH)₂ had no significantenhancing effect on the sorbent reactivity toward SO₂ during in-furnacesorbent injection experiments.

U.S. Pat. No. 4,191,115 discloses a method for enhancing the SO₂absorption of limestone used during a fluidized bed combustion ofcarbonaceous fuels. According to the '115 patent, limestone is sprayedwith a mixture of iron sulfate and iron sulfite in a separate chamberbefore the limestone is injected into the fluidized bed combustor. Thesulfation data presented in the '115 patent indicate that 3 hours areneeded to obtain particle sulfation levels of 60%.

Thus, the state of the art indicates that urea yields no improvedresults for SO₂ removal, and that iron is not an effective promoter forsulfur sorbents.

In light of the above, it can be seen that there is a need for a sulfursorbent composition which is not costly to prepare and which does notrequire expensive starting materials.

It is therefore the principal object of the present invention to providea process for preparing a sulfur sorbent composition which is effectiveand inexpensive to produce.

It is still a further object of the present invention to provide aprocess for producing a sorbent using iron and urea additives to enhanceSO₂ removal.

Other objects and advantages will become readily apparent to a personskilled in the art upon consideration of the following description ofthe invention.

SUMMARY OF THE INVENTION

The foregoing objects and advantages are obtained by a process for theproduction of a sulfur sorbent composition in a mixer having a mixerpaddle and an energy supply for supplying energy to the mixer comprisinghydrating an alkaline earth metal oxide in an aqueous solutioncontaining a promoting additive selected from a group consisting of ureaand mixtures of urea with a water soluble iron salt under high intensitymixing conditions with said mixer wherein said mixer is operated underthe following parameters: mixer paddle tip velocity of at least 500ft/min; and energy input to the mixer of at least 3.5 kW-h per ton ofsorbent. This energy input is measured in terms of total energy input tothe mixer.

According to the invention, a sulfur sorbent composition is producedhaving the following physical and chemical properties:

alkaline earth metal (wt %)--about 40-52;

molar ratio of promoting additive to alkaline earth metal--0.001-0.2;

bulk density (g/ml)--about 0.25-0.95;

surface area (m² /g)--about 3-75;

pore volume (cc/g)--about 0.02-0.20;

mean particle size (μm)-<about 6.0

Preferred alkaline earth metal oxides include calcium oxide, magnesiumoxide, and mixtures thereof.

The preferred promoting additive is a mixture of urea and an iron saltselected from a group consisting of ferrous sulfate, ferric sulfate,ferrous chloride, ferric chloride, ferrous nitrate, ferric nitrate, andmixtures thereof.

The mixing intensity is preferably defined by a mixer paddle tipvelocity exceeding about 1000 ft/min, and more preferably still in therange of about 6000 to 9000 ft/min. Energy is preferably supplied to themixer at a rate of at least 3.5 kW-h per ton of sorbent, more preferablyat least 4.0 kW-h/ton of sorbent, and at a mixing time of less thanabout 15 seconds.

BRIEF DESCRIPTION OF THE DRAWING

A detailed description of the invention follows, with reference to theaccompanying drawing, in which:

FIG. 1 is a graph illustrating the relation between mixing intensity andSO₂ removal.

DETAILED DESCRIPTION

The present invention is drawn to a process for producing a sorbent foruse in reducing SO₂ contained in an effluent stream of gas and aresultant sorbent product. More particularly, the process includes thesteps of dissolving a promoting additive in water to provide an aqueoussolution and hydrating an alkaline earth metal oxide with the aqueoussolution under high mixing intensity to provide a sorbent havingenhanced SO₂ reactivity.

According to the invention, the promoting additive is preferably ureawhich may be mixed with one of more water soluble iron salts. While manyiron salts are suitable, such as, for example, ferrous sulfate, ferricsulfate, ferrous chloride, ferric chloride, ferrous nitrate, ferricnitrate, and mixtures thereof, ferrous sulfate is particularly suitablebecause of its low cost.

Suitable alkaline earth metal oxides include calcium oxide, magnesiumoxide, and mixtures thereof. Improved results are obtained, according tothe invention, when the metal oxide is ground so as to provide a grainsize wherein 90% of the particles are smaller than about 250 microns.

Water is preferably provided for the hydration at least instoichiometric amounts, that is, 32 lb of water per 100 lb of CaO. Thepreferred upper limit for water is set by the maximum amount of waterwhich can be used to produce a dry Ca(OH)₂ product. A sufficiently dryproduct can be obtained when up to 75 lbs of water are used per 100 lbsof CaO. The ratio by weight of water to CaO is, therefore, preferablybetween about 32:100 to 75:100. A preferred ratio of water to CaO isbetween about 45:100 to 70:100.

As a promoting additive, urea is added to the hydration water in amountssufficient to provide a molar ratio of urea to calcium of between about0.001 to 0.2, preferably between about 0.005 to 0.075. Ferrous sulfateis also preferably added to the hydration water in amounts sufficient toprovide a molar ratio of iron to calcium of between about 0.001 to 0.2,preferably between about 0.005 to 0.075.

Once the above promoting additives are completely dissolved in thehydration water, the resulting solution is added to a mixer containingthe calcium oxide.

It is critical, according to the invention, to provide a high intensitymixing in order to obtain a final product sorbent from the aforesaidingredients having improved reactivity to SO₂. Conventional commercialquicklime hydration plants use blenders typically having paddles. Themixing intensity used in such conventional hydration procedures can bedefined based on a tip velocity of the mixing paddle and energy suppliedto the blender. Conventional quicklime hydration is typically carriedout at energy or power inputs of about 0.4 kW-h/ton of sorbent andmixing paddle tip velocity of about 155 to 315 ft/min. with mixing timesexceeding 5 minutes.

At conventional mixing intensity, urea and iron are ineffective aspromoters for calcium oxide based sulfur sorbent. It has been found,according to the invention, that high intensity mixing, characterized bya mixer paddle tip velocity of at least about 500 ft/min, preferably atleast about 1000 ft/min, most preferably between about 6000 to 9000ft/min, and an energy input to the mixer of at least about 3.5 kW-h/tonof sorbent, preferably at least about 4.0 kW-h/ ton of sorbent, andmixing times less than about 15 seconds, provide sorbents in which,surprisingly, urea is a much more effective promoter and urea/iron is anextremely effective promoter.

Suitable high intensity mixing can be obtained, according to theinvention, by a high speed single rotor mixer. Such a continuous mixerhas a single rotating shaft that carries paddles enclosed in acylindrical shell. This type of mixer can provide a tip velocity of atleast about 500 ft/min with an energy requirement of at least about 3.5kW-h/ton, under normal mixer loading conditions. The energy ratescontained herein refer to total energy supplied to the mixer by theenergy supply, and not net energy (net energy =energy loaded-energyunloaded).

As can be seen, the mixing intensity intended for use with the presentinvention is markedly higher than that conventionally utilized inquicklime hydration plants. This increased mixing intensity provides aurea or urea/iron promoter sorbent having an improved reactivity to SO₂as will be illustrated by the following Examples.

The high intensity mixing is preferably carried out with the hydrationcomponents at an initial temperature below about 100° C., and hydrationpressure preferably less than about 10 atmospheres, more preferablyabout 1 atmosphere.

When high mixing intensity is applied to the promoter/calcium oxidemixture, the mixing procedure typically takes less than about 15seconds. The sorbent at this point may still contain excess water.Accordingly, a two stage process is preferably utilized to remove excesswater. The first stage is, according to the invention, the applicationof high intensity mixing to the aqueous solution and the quicklime in asuitable mixer. This mixing normally lasts for a period of time lessthan about 15 seconds. The second stage includes passing thesolution-quicklime mixture to a seasoning chamber where the hydrationreaction is completed under low intensity mixing conditions and whereexcess water is steamed off for a period of time generally less thanabout 10 minutes.

This two stage procedure ensures a dry product despite the shortreaction time dictated by the high intensity mixing.

According to this procedure, a promoted sorbent product is formed whichyields excellent reduction of SO₂ from streams of effluent gas.

The sorbent product comprises a hydrated alkaline earth metal oxidecomposition containing a promoting additive. As stated above, thealkaline earth metal is preferably selected from a group consisting ofcalcium oxide, magnesium oxide, and mixtures of calcium oxide andmagnesium oxide.

The promoting additive is preferably either urea or mixtures of urea andan iron salt such as, for example, ferrous sulfate, ferric sulfate,ferrous chloride, ferric chloride, ferrous nitrate, ferric nitrate, andmixtures thereof. As stated above, ferrous sulfate is the presentlypreferred iron salt because it is relatively inexpensive.

The sulfur sorbent is characterized by the following physical andchemical properties:

calcium (wt %)--about 40-52%;

molar ratio of promoting additive to calcium--about 0.001-0.2;

bulk density (g/ml)--about 0.25-0.95;

surface area (m² /g)--about 3-75;

pore volume (cc/g)--about 0.02-0.20; and

mean particle size (μm)--<about 6.0.

More preferably, the sulfur sorbent composition will have the followingproperties:

bulk density (g/ml)--about 0.35-0.75;

surface area (m² /g)--about 5-25;

pore volume (cc/g)--about 0.05-0.14; and

mean particle size (μm)--≦about 4.

With reference to the molar ratio of promoting additive to calcium, apreferred promoting additive is urea at a molar ratio to Ca of about0.001 to 0.2 and ferrous sulfate in sufficient amounts to provide amolar ratio of iron to Ca of about 0.001 to 0.2. More preferably, eachof these molar ratios is about 0.005 to 0.075.

In use, the sorbent according to the invention is injected or admixed inparticle form with an effluent gas stream at a point preferablydownstream of the combustion zone. The injection is preferably carriedout at a point in the stream where the temperature of the stream isbetween about 900° C. to 1200° C., and more preferably, where thetemperature is about 1050° C. to 1200° C. In a typical boiler, thecontact time of the sorbent particle with the effluent gas at thistemperature is generally less than about 2 seconds. Sorbent ispreferably admixed with the effluent gas in order to provide a ratio ofalkaline earth metal to sulfur in the effluent gas stream of about threeor less. The sorbent according to the invention exhibits enhanced SO₂reactivity under this time constraint.

Two Examples follow which are presented in order to demonstrate theimprovements of the present process and sorbent over those of the priorart.

EXAMPLE I

This example demonstrates the enhanced results obtained by the promotedsorbent of the present invention prepared using increased mixingintensity according to the present invention.

Three sorbents were prepared, and identified as sorbents A, B and C, inorder to compare the effectiveness of sorbents prepared according to theprocedures of U.S. Pat. No. 4,731,233 (sorbents A and B), using knownhydration techniques, to the effectiveness of sorbents preparedaccording to the present invention (sorbent C). These sorbents wereprepared as follows:

Sorbent A

100 grams of calcium oxide were hydrated with 65 grams of water. Thesefigures are identical to those employed in the '233 patent in Test No. 1of Group No. 1 in Example 1. The sorbent was prepared following standardprocedures for preparation of hydrates, that is, the solution wascombined with calcium oxide and the mixture was stirred withconventional levels of intensity (tip velocity of 251 ft/min., energyinput of 1.1 kW-h per ton of sorbent) to assure that all calcium oxidewas converted to calcium hydroxide by reaction with water.

Sorbent B

100 grams of calcium oxide were hydrated in 65 grams of a water solutioncontaining 5.25 grams of urea. These figures are identical to those usedin Test Nos. 2 and 3 of Test Group No. 1 and all of the tests of TestGroup No. 2 as set forth in Example 1 of the '233 patent. This sorbentwas also prepared following conventional procedures for preparation ofhydrates. Thus, the solution was combined with the calcium oxide andmixed at conventional mixing intensities (tip velocity of 251 ft/min.,energy input of 1.1 kW-h per ton) sufficient to assure that all calciumoxide was converted to calcium hydroxide by reaction with water.

Sorbent C

This sorbent was prepared, according to the present invention, byhydrating 100 grams of calcium oxide and 65 grams of a water solutioncontaining 5.25 grams of urea. These amounts are identical to those usedfor sorbent B above. The solution and the calcium oxide were fed to thecontinuous mixer, and stirred at a mixing intensity much higher thanthose used in conventional processes. The mixing intensity which wasemployed is defined by a tip velocity of the mixing blades of 3533ft/min. The energy supplied to the mixer for Sorbent C was 41 kW-h perton.

Testing conditions employed in the '233 patent were reproduced inaccordance with the teachings of that patent. Thus, the combustionproducts were generated by burning known amounts of natural gas and airin an 8 inch diameter combustion tunnel. The SO₂ at the point where thesorbent was injected was controlled by adding SO₂ to the natural gas.The nitrous oxide at the point of sorbent injection was controlled byadding NH₃ to the natural gas, a portion of which was converted tonitrous oxide during combustion of the natural gas. The temperature atthe point of sorbent injection was measured by a thermocouple andcontrolled by (1) water cooled heat exchanger tubes upstream of thepoint of the sorbent injection, (2) the amount of natural gas burned and(3) backfire burners surrounding the combustion tunnel. The amount ofoxygen in the combustion products was controlled by varying the relativeamounts of gas and air. The sorbent was contacted with the stream ofcombustion products by using a screw feeder to add the sorbent in an airstream.

The testing summarized in Table 1 was carried out at two testingconditions, identified in the table as testing conditions 1 and 2.

Sorbent performance is reported in terms of ΔSO₂ at Ca/S=2. This valueis calculated according to the following equation: ##EQU1##

With this equation, it is possible to standarize the various resultsobtained from experiments using different ratios of calcium to sulfate.Obviously, higher values of ΔSO₂ imply a larger removal of SO₂ and,therefore, a more reactive material. Sorbents promoted with urea andhydrated under conditions of high mixing intensity, in accordance withthe present invention, yield values of ΔSO₂, exceeding 65%. As can beseen in Table 1, the preferred process temperature range of 1050° C. to1200° C. yields a more markedly improved ΔSO₂.

                                      TABLE 1                                     __________________________________________________________________________                                 Combustor Conditions                                     Hydrated Sorbent         Res.                                                                              O2                                       Test    CaO                                                                              H2O/urea                                                                            Tip vel                                                                            Mix Ener                                                                             T   time                                                                              vol %                                    Cond.                                                                             Sorb.                                                                             gm sol gm/gm                                                                           (ft/min)                                                                           (kw/ton/hr)                                                                          (°C.).                                                                     (sec)                                                                             (dry)                                    __________________________________________________________________________    1   A   100                                                                              65/0  251  1.13    954                                                                              0.38                                                                              9.9                                      1   B   100                                                                              65/5.25                                                                             251  1.13    954                                                                              0.38                                                                              9.9                                      1   C   100                                                                              65/5.25                                                                             3533 41      954                                                                              0.38                                                                              9.9                                      2   A   100                                                                              65/0  251  1.13   1121                                                                              0.35                                                                              7.9                                      2   B   100                                                                              65/5.25                                                                             251  1.13   1093                                                                              0.35                                                                              7.8                                      2   C   100                                                                              65/5.25                                                                             3533 41     1093                                                                              0.35                                                                              7.9                                      __________________________________________________________________________            Sorbent Injection                                                                        Input Output                                                                              Removal                                                Ratios     SO2                                                                              NO SO2                                                                              NO ΔSO2 @                                   Test    Ca/SO2                                                                             Urea/NO                                                                             ppm                                                                              ppm                                                                              ppm                                                                              ppm                                                                              Ca/S = 2                                                                            ΔNOx                               Cond.                                                                             Sorb.                                                                             mol ratio                                                                          mol ratio                                                                           (dry)                                                                            (dry)                                                                            (dry)                                                                            (dry)                                                                            %     %                                        __________________________________________________________________________    1   A   1.66 0     2480                                                                             495                                                                              1240                                                                             480                                                                              60     3                                       1   B   2.16 0.47  2400                                                                             505                                                                               780                                                                             170                                                                              62    66                                       1   C   2.01 0.43  2360                                                                             505                                                                               760                                                                             270                                                                              67    47                                       2   A   1.42 0     2228                                                                             488                                                                              1280                                                                             473                                                                              60     3                                       2   B   2.52 0.49  2190                                                                             515                                                                               460                                                                             333                                                                              63    35                                       2   C   1.91 0.41  2480                                                                             533                                                                               720                                                                             355                                                                              74    33                                       __________________________________________________________________________

By comparing sulfur removal results for sorbents A and B, underconditions 1 and 2, it is clear that the addition of urea to the sorbentemploying standard hydration procedures has minimal impact, if any, onthe reaction between SO₂ and CaO. This is the same conclusion reached inthe '233 patent.

By comparing results from sorbents A and C, however, a clear enhancementin sulfur removal is observed. This improvement is more drastic underthe preferred conditions represented by test condition 2. Althoughsorbents B and C appear to have the same composition, it is clear thatthe special hydration conditions disclosed as part of the process of thepresent invention (high mixing intensity) must provide some differencebetween the sorbents as sorbent C yields on enhanced reactivity to SO₂.

EXAMPLE II

This Example demonstrates the improved performance of sorbents promotedwith urea additives, and the further improved performance of sorbentpromoted with urea/FeSO₄ additives, when such sorbents are preparedunder conditions of high intensity mixing.

The starting material for all sorbents of this example was a pulverizedcommercial pebble Linwood calcium oxide having a particle size at least90% below 250 microns. Table 2 sets forth the compositions, hydrationconditions and morphology for 11 sorbents prepared and tested.

                                      TABLE 2                                     __________________________________________________________________________    Summary of Sulfation Results                                                  __________________________________________________________________________    Sorbent        Hydration Conditions                                                                             Reaction Conditions                         Composition    Tip  Mix    (Vel) · (E)    ΔSO2 @               Sorbent                                                                            Fe/Ca                                                                              Urea/Ca                                                                            Vel  Energy (ft/min) ·                                                                  T  Ca/S SO2 in                                                                            SO2 out                                                                            Ca/S = 2                   Number                                                                             (molar)                                                                            (molar)                                                                            (ft/min)                                                                           (Kw/ton/hr)                                                                          (Kw/ton/h)                                                                           (°C.)                                                                     (molar)                                                                            (ppm)                                                                             (ppm)                                                                              (%)                        __________________________________________________________________________    1    0    0     251 1.13     284  1121                                                                             1.42 2228                                                                              1280 60                         2    0    0    1177 39.8    46845 1093                                                                             2.24 2360                                                                              740  61                         3    0    0    3532 41.2   145518 1121                                                                             2.44 2365                                                                              610  61                         4    0    0.05  251 1.13     284  1093                                                                             2.52 2190                                                                              460  63                         5    0    0.05 1177 39.8    46845 1093                                                                             2.02 2480                                                                              780  68                         6    0    0.05 3532 41.2   145518 1093                                                                             1.91 2480                                                                              720  74                         7    0.03 0    3532 41.2   145518 1100                                                                             1.71 2500                                                                              1367 53                         8    0.03 0.05  251 1.13     284  1093                                                                             1.59 2480                                                                              1435 53                         9    0.03 0.05 1177 39.8    46845 1121                                                                             1.63 2400                                                                              1050 69                         10   0.03 0.05 3532 41.2   145518 1147                                                                             1.48 2080                                                                              849  80                         11   0.03 0.05 5299 47.8   253292 1121                                                                             2.05 2240                                                                              320  84                         __________________________________________________________________________                                 Sorbent Morphology                                                            Calcined    Fresh                                                                 Pore        Pore                                                                              Bulk                                                                              Real                                             Sorbent                                                                            S.A.                                                                              Vol.                                                                              Poros.                                                                            S.A.                                                                              Vol.                                                                              Dens.                                                                             Dens.                                            Number                                                                             (m2/g)                                                                            (cc/g)                                                                            ε                                                                         (m2/g)                                                                            (cc/g)                                                                            (g/ml)                                                                            (g/ml)                   __________________________________________________________________________                            1    17.3                                                                              0.102                                                                             0.256                                                                             24.9                                                                              0.135                                                                             n.a.                                                                              2.15                                             2    n.a.                                                                              n.a.                                                                              n.a.                                                                              36.1                                                                              0.158                                                                             0.48                                                                              2.75                                             3    17.2                                                                              0.106                                                                             0.263                                                                             35.2                                                                              0.192                                                                             0.54                                                                              2.16                                             4    21.3                                                                              0.147                                                                             0.332                                                                             32.9                                                                              0.133                                                                             0.56                                                                              2.73                                             5    19.1                                                                              0.145                                                                             0.329                                                                             39.0                                                                              0.157                                                                             0.62                                                                              2.84                                             6    21.1                                                                              0.155                                                                             0.344                                                                             23.9                                                                              0.128                                                                             0.52                                                                              2.14                                             7    na  na  na  na  na  na  na                                               8    14.7                                                                              0.103                                                                             0.260                                                                             32.2                                                                              0.110                                                                             0.62                                                                              2.16                                             9    14.9                                                                              0.117                                                                             0.284                                                                             14.1                                                                              0.069                                                                             0.60                                                                              2.64                                             10   n.a.                                                                              n.a.                                                                              n.a.                                                                              n.a.                                                                              n.a.                                                                              n.a.                                                                              n.a.                                             11   15.1                                                                              0.121                                                                             0.291                                                                             20.0                                                                              0.094                                                                             0.55                                                                              2.73                     __________________________________________________________________________     na -- no data taken.                                                     

The SO₂ capture performance of the sorbent presented in this example wasmeasured in the same combustion tunnel used in Example I. The flue gastemperature was maintained at about 1100° C. The oxygen level wasmaintained at about 3.5 % by volume (on a dry basis), and the residencetime for the sorbent was about 0.38 seconds. These conditions aresimilar to those encountered with dry sorbent injection in commercialboilers.

These sorbents, as indicated in Table 2, were prepared at bothconventional and high mixing intensities, and were prepared usinghydration solutions which were non-promoted, promoted with urea only,promoted with iron only, and promoted with combinations of urea andiron.

FIG. 1 sets forth the relationship between mixing intensity hererepresented by a product of tip velocity times mixing energy, versus thepercentage of SO₂ removal at a Ca/S ratio of 2. As can be seen, theincreased mixing intensity had little effect on an unpromoted sorbent.Further, the sorbent in which only iron was added demonstrated adecrease in SO₂ removal. Confirming the improvement of the presentinvention, however, the sorbent promoted with urea and hydrated at highmixing intensity showed a marked improvement in SO₂ removal. Further,the sorbent promoted with a combination of urea and FeSO₄ and hydratedat high mixing intensity (sorbents 9, 10 and 11) demonstrated an evenmore drastic improvement (ΔSO₂ =75% and greater) over SO₂ removal ratesobtained by conventionally prepared sorbents.

Thus disclosed is a process for producing a sorbent for treatment ofeffluent gas streams. The process utilizes conditions of high mixingintensity which yields a sulfur sorbent product exhibiting, as shown inTable 2, a 30-60% improvement in sulfur capture as compared to sorbentsproduced conventionally.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:
 1. A process for the production of a sulfur sorbentcomposition in a mixer having a mixer paddle and an energy supply forsupplying energy to the mixer comprising hydrating under high intensitymixing conditions an alkaline earth metal oxide in an amount of about 40to 52% by weight in an aqueous solution containing a promoting additivewherein the molar ratio of promoting additive to alkaline earth metal insaid alkaline earth metal oxide is about 0.001 to 0.2, said promotingadditive being selected from a group consisting of urea and mixtures ofurea with a water soluble iron salt so as to produce a sulfur sorbentcomposition, wherein said mixer is operated under the followingparameters;a mixer paddle tip velocity of at least about 500 ft/min; anenergy input to the mixer of at least about 3.5 kW-h per ton of sorbent;and a mixing time of less than about 15 seconds.
 2. A process accordingto claim 1, comprising hydrating said alkaline earth metal oxide so asto produce a sulfur sorbent composition further characterized by thefollowing physical and chemical properties:bulk density (g/ml)--about0.25-0.95; surface area (m² /g)--about 3-75; pore volume (cc/g)--about0.02-0.20; and mean particle size (μm)--<about 6.0.
 3. A processaccording to claim 1, comprising hydrating said alkaline earth metaloxide so as to produce a sulfur sorbent composition furthercharacterized by the following physical and chemical properties:bulkdensity (g/ml)--about 0.35-0.75; surface area (m² /g)--about 5-25 porevolume (cc/g)--about 0.05-0.14; and mean particle size (μm)--≦about 4.0.4. A process according to claim 1, wherein the alkaline earth metaloxide is selected from a group consisting of calcium oxide, magnesiumoxide, and mixtures of calcium oxide and magnesium oxide.
 5. A processaccording to claim 1, wherein said alkaline earth metal oxide is groundto a particle size wherein at least 90% of particles contained thereinare no larger than about 250 microns.
 6. A process according to claim 1,wherein alkaline earth metal oxide is added to the aqueous solution at aratio by weight of water to alkaline earth metal oxide of between about32:100 to 75:100.
 7. A process according to claim 1, wherein alkalineearth metal oxide is added to the aqueous solution at a ratio by weightof water to alkaline earth metal oxide of between about 45:100 to70:100.
 8. A process according to claim 1, wherein hydration componentsare fed to the mixer at temperatures below about 100° C and a pressureless than about 10 atmospheres.
 9. A process according to claim 1,wherein hydration components are fed to the mixer at temperatures belowabout 100° C. and a pressure of about 1 atmosphere.
 10. A processaccording to claim 1, further comprising hydrating said alkaline earthmetal oxide in said aqueous solution in a two stage continuous procedurecomprising a first stage of applying said high intensity mixingconditions for a period of less than about 15 seconds and a second stageof steaming off excess water for a period of less than about tenminutes.
 11. A process according to claim 1, wherein said mixer isoperated at a mixer paddle tip velocity of at least about 1000 ft/min.12. A process according to claim 1, wherein said mixer is operated at amixer paddle tip velocity of between about 6000 to 9000 ft/min and anenergy input of at least about 4 kW-h per ton of sorbent.
 13. A processaccording to claim 1, wherein said hydrating step comprises dissolvingsaid promoting additive in said aqueous solution and mixing saidalkaline earth metal oxide with said aqueous solution in said mixerunder said high intensity mixing conditions.
 14. A process according toclaim 1, wherein the promoting additive is a mixture of urea and a watersoluble iron salt selected from a group consisting of ferrous sulfate,ferric sulfate, ferrous chloride, ferric chloride, ferrous nitrate,ferric nitrate, and mixtures thereof.
 15. A process according to claim14, preparing an aqueous solution containing urea and iron salt; andmixing said aqueous solution with calcium oxide, said urea being addedto the aqueous solution so as to provide a molar ratio of urea tocalcium of between about 0.001 to 0.2 and said iron salt being added tothe aqueous solution so as to provide a molar ratio of iron to calciumof between about 0.001 to 0.2.
 16. A process according to claim 14,preparing an aqueous solution containing urea and iron salt; and mixingsaid aqueous solution with calcium oxide, said urea being added to theaqueous solution so as to provide a molar ratio of urea to calcium ofbetween about 0.005 to 0.075 and said iron salt being added to theaqueous solution so as to provide a molar ratio of iron to calcium ofbetween about 0.005 to 0.075.
 17. A sulfur sorbent compositioncomprising a hydrated alkaline earth metal oxide composition containinga promoting additive comprising a mixture of urea with a water solubleiron salt, the sorbent being characterized by the followingproperties:alkaline earth metal (wt.%)--about 40-52; and molar ratio ofpromoting additive to alkaline earth metal--about 0.001-0.2;said sorbentproviding at least a 65% reduction in sulfur content when contacted witha sulfur bearing effluent stream at a temperature of between 900° C. to1200° C. for a period of less than 2.0 seconds.
 18. A sulfur sorbentcomposition according to claim 17, the sorbent being furthercharacterized by the following physical and chemical properties:bulkdensity (g/ml)--about 0.25-0.95; surface area (m² /g)--about 3-75; porevolume (cc/g)--about 0.02-0.20; and mean particle size (μm)--<about 6.0.19. A sulfur sorbent composition according to claim 17, the sorbentbeing further characterized by the following physical and chemicalproperties:bulk density (g/ml)--about 0.35-0.75; surface area (m²/g)--about 5-25 pore volume (cc/g)--about 0.05-0.14; and mean particlesize (μm)--about--≦4.0.
 20. A sulfur sorbent composition according toclaim 17, wherein the alkaline earth metal oxide is selected from agroup consisting of calcium oxide, magnesium oxide, and mixtures ofcalcium oxide and magnesium oxide.
 21. A sulfur sorbent productaccording to claim 17, wherein the promoting additive is a mixture ofurea and a water soluble iron salt selected from a group consisting offerrous sulfate, ferric sulfate, ferrous chloride, ferric chloride,ferrous nitrate, ferric nitrate, and mixtures thereof, said sorbentproviding at least a 75% reduction in sulfur content when contacted witha sulfur bearing effluent stream.
 22. A sulfur sorbent compositionaccording to claim 21, wherein a molar ratio of urea to alkaline earthmetal in said alkaline earth metal oxide is between about 0.001 to 0.2and a molar ratio of iron to alkaline earth metal is between about 0.001to 0.2.
 23. A sulfur sorbent composition according to claim 21, whereina molar ratio of urea to alkaline earth metal is between about 0.005 to0.075 and a molar ratio of iron to alkaline earth metal in said alkalineearth metal oxide is between about 0.005 to 0.075.
 24. A sulfur sorbentcomposition resulting from a process of hydrating under high intensitymixing conditions and alkaline earth metal oxide in an amount of about40 to 52% by weight in an aqueous solution containing a promotingadditive consisting essentially of urea wherein the molar ratio ofpromoting additive to alkaline earth metal in said alkaline earth metaloxide is about 0.001 to 0.2, said high intensity mixing conditionscomprises a mixer paddle tip velocity of at least about 500 ft/min, anenergy input to the mixer of at least about 3.5 kW-h per ton of sorbentand a mixing time of less than about 15 seconds, the sulfur sorbentbeing characterized by the following chemical and physicalproperties;alkaline earth metal of about 40-52 wt.%; molar ratio of ureato alkaline earth metal of about 0.001 to 0.2; bulk density (g/ml) ofabout 0.25 to 0.95; surface area (m² /g) of about 3 to 75; pore volume(cc/g) of about 0.02 to 0.20; mean particle size (μm) of < about 6.0;and said sorbent providing at least a 65% reduction in sulfur contentwhen contacted with a sulfur bearing effluent stream at a temperature ofbetween 900° C. to 1200° C. for a period of less than 2.0 seconds.